1. Field of the Invention
The present invention relates generally to multilayer capacitors, and more particularly, to a multilayer capacitor having high Q characteristics in a high frequency band of several tens MHz to several GHz.
2. Description of the Prior Art
In order to improve the performance of an electronic equipment, it is essential to improve Q characteristics of a multilayer capacitor in the above described high-frequency band.
Therefore, in the conventional multilayer capacitor, the Q characteristics are enhanced by decreasing a capacitance acquired by one dielectric layer and arranging a lot of dielectric layers in parallel to decrease ESR (equivalent series resistance) of an inner electrode.
Referring to FIGS. 6 to 10, the structures and the problems of the conventional multilayer capacitor will be described more concretely. A capacitor having a low capacitance of approximately 1 pF to 10 pF is taken as an example. In a multilayer capacitor 1 shown in FIG. 6, a pair of inner electrodes 3a and 3b is arranged so as to be partially overlapped with each other while being separated by a dielectric layer 2a inside of a dielectric body 2. The inner electrode 3a is electrically connected to an outer electrode 4b, while the inner electrode 3b is electrically connected to an outer electrode 4b. In this structure, it is possible to ensure a capacitance but it is difficult to enhance Q characteristics.
Accordingly, a multilayer capacitor 11 has been proposed in which more inner electrodes are arranged in a dielectric body 12, as shown in FIG. 7. In this multilayer capacitor 11, a plurality of inner electrodes 13a to 13e are arranged.
Furthermore, a multilayer capacitor 21 has been proposed in which the thickness of a dielectric layer 22a between inner electrodes 23a and 23b is increased, as shown in FIG. 8. Further, when it is desired to particularly enhance Q characteristics, a structure has been proposed in which the number of inner electrodes is increased and some of the inner electrodes are constructed as so-called double electrodes 33a and 33b, as shown in FIG. 9. That is, a multilayer capacitor in which an inner electrode 13c in the multilayer capacitor 11 shown in FIG. 7 is of double electrode construction corresponds to a multilayer capacitor 31 shown in FIG. 9. 33c to 33f also denote inner electrodes.
However, the ESR is small in a low frequency region while being large in a high frequency region. More specifically, the increase of eddy currents 42 and 43 produced when a current flows in an inner electrode 41 in the direction of an arrow I, as shown in FIG. 10, causes the ESR to be increased. As a result, in the above described conventional multilayer capacitors 11, 21 and 31, sufficiently high Q characteristics cannot be achieved.